Chromosome studies in hypoptopomatinae ( pisces , siluriformes, loricariidae): ii. Zz / zw sex-chromosome system, b chromosomes, and constitutive heterochromatin differentiation in microlepidogaster leucofrenatus - Andreata, A A; Almeida-Toledo, Lurdes Foresti de; Oliveira, C.; Toledo Filho, Sílvio de Almeida (Cytogenetics and Cell Genetics, 1993)